When a variety of wireless communication systems utilize different spectrums, supporting high-speed multimedia service by allocating a new frequency band is limited because of lack of the frequencies. To address the frequency deficiency, a Cognitive Radio (CR) technique for raising the frequency utilization is drawing attention.
While a Primary User (PU) of the existing frequency license is not using the corresponding band, the CR technique enables a Secondary User (SU) to share the band. It should protect the PUs and ensure quality of service of the SUs (hereafter, referred to as self coexistence). To provide broadband wireless access services over the area ranging from tens of km to 100 km, Institute of Electrical and Electronics Engineers (IEEE) 802.22 standardization for sharing the currently allocated broadcast band based on the CR is under process.
In the CR system with the self coexistence function, a base station detects at least one unused channel of the primary/licensed system and communicates over the detected channel. When a plurality of CR systems spatially coexists, the CR systems exchange a Coexistence Beacon Protocol (CBP) packet to raise the spectrum utilization. To facilitate the self coexistence function, the CR system mostly adopts a superframe structure. For example, the IEEE 802.22 standard defines sixteen (16) frames in the time axis as one superframe.
To handle the coexistence problem in communication systems based on the current CR function, algorithms such as spectrum etiquette, interference-free scheduling, and spectrum contention are suggested. The spectrum etiquette algorithm selects a channel causing little interference or a channel causing the least interference to neighboring base stations. The interference-free scheduling algorithm schedules not to cause the channel interference in the channel resource allocation for the uplink and the downlink. The spectrum contention algorithm makes the base stations occupy the channel through the contention when the channels are insufficient.
In the CR system operation, when the PU appears in the base station and utilizes the channel used by the base station, the base station can no longer use the channel. Therefore, the channels in the base station may be insufficient to degrade the quality of service or give rise to the out-of-service. However, the conventional CR based communication systems cannot suggest more enhanced solutions for the effective utilization of the channel resources between the base stations. In this respect, research is sought.